1. Field of the Invention
The present invention relates to a temperature sensor exhibiting excellent response and to a production control method therefor. More particularly, the present invention relates to a temperature sensor used for measuring the temperature of exhaust gas of a combustor or an internal combustion engine, the sensor being suitable for use at high temperature; and to a production control method for the sensor.
2. Description of the Related Art
A Pt resistor or a bulk thermistor element formed from a sintered oxide is conventionally used in a temperature sensor. However, the electrical characteristics of such a temperature sensor are easily deteriorated, by poisoning with carbon or phosphorus contained in exhaust gas or variation in partial pressure of oxygen. Therefore, when a bulk thermistor element is used, deterioration of electrical characteristics is prevented by shielding the element from the outside air by use of a glass material or a protective tube formed, for example, from stainless steel. When a Pt resistor is used, deterioration of electrical characteristics is prevented by sealing with a glass material, and the Pt resistor is formed in a certain pattern on an insulating substrate.
When a bulk thermistor element is to be used in an automobile, which produces vigorous vibration, the element is secured at a center portion of a protective tube using a filler such as cement or by means of caulking. This is to prevent breakage of the element, which occurs when the element contacts the protective tube as a result of strong vibration.
In order to effect high-speed combustion control of a combustor or an internal combustion engine, there is a need to enhance the response of a thermosensitive element. Several methods for enhancing the response of a thermosensitive element have been proposed, including a method in which the thickness of a protective tube as described above is reduced to thereby reduce, as much as possible, excess heat capacity of the tube (Japanese Patent Application Laid-Open (kokai) No. 9-189618), and a method in which the thickness of a thermosensitive element is reduced in order to enhance conductivity of heat from the outside air (Japanese Patent Application Laid-Open (kokai) No.9-218110).
In the aforementioned conventional method, since a thermistor element is protected by a layer having a relatively low thermal conductivity, such as a stainless steel layer, a glass layer, or a cement layer, a certain time elapses before heat of the exhaust gas reaches the thermistor element. Furthermore, since an air layer is present between such a layer and the thermistor element, conduction of heat to the thermistor element is lowered. Therefore, in the conventional method, it is difficult to further enhance the response of the thermistor element. Meanwhile, although a Pt resistor provided on an insulating substrate exhibits excellent response, a glass seal provided on the resistor is resistant to a temperature of up to about 600xc2x0 C. Therefore, the Pt resistor is only applicable to measurement of a limited range of the temperature of exhaust gas of an internal combustion engine, which may reach 1,000xc2x0 C.
Response of a thermosensitive element such as a thermistor element may be enhanced by miniaturizing the element to thereby reduce the heat capacity thereof. However, in order to obtain the desired characteristics, an electrode must be applied to the thermosensitive element with high accuracy. As a result, productivity decreases and production costs increase. Therefore, it is difficult to miniaturize the thermosensitive element.
In view of the foregoing, an object of the present invention is to provide a temperature sensor exhibiting excellent response and a production control method therefor. More particularly, an object of the present invention is to provide a temperature sensor used for measuring the temperature of exhaust gas of a combustor or an internal combustion engine, the sensor adapted for use at high temperature; and a production control method for the sensor.
The above objective has been achieved by providing a temperature sensor comprising a thermosensitive element and a ceramic body having a hollow section which surrounds the thermosensitive element in an airtight manner.
The above objective has also been achieved by providing a production control method for use in manufacturing production lots of a temperature sensor including a thermosensitive element and a ceramic body having a hollow section which surrounds the thermosensitive element in an airtight manner, the ceramic body having a substrate side and a heat-sensing surface side, and the thermosensitive element being disposed on the heat-sensing surface side of the ceramic body, which method comprises determining variation in response of the thermosensitive element among production lots in a preliminary test, and adjusting, on the basis of the results of the test, the thickness of the heat-sensing surface side ceramic layer of the ceramic body.